GB2060376A - Fire protection system - Google Patents

Abstract

A fire protection system comprises a fire extinguisher (8), pneumatically operable actuation means (18) on the fire extinguisher (8) for triggering the extinguisher, an elongatetube (12) containing a temperature responsive gas-evolving substance (40) and a conduit (16) connecting the tube (12) to the actuation means for transmitting gas pressure to the actuation means. The gas-evolving substance (40) is selected to generate, when the temperature about the tube (12) attains a critical value within a predictable range, a quantity of gas which develops a pressure in the conduit (16) sufficient to operate the actuation means (18). <IMAGE>

Description

SPECIFICATION Fire protection system This invention relates to a fire protection system which has special utility in relatively harsh environments.

The conventional fire protection system employs detectors sensitive to a prescribed local temperature or temperature gradient, or to the presence of smoke. These detectors tend to be unsuitable for harsh environments, where they are susceptible to high false alarm rates and a relatively short life.

Temperature responsive detectors typically include finely spaced contacts which are too readily bridged by water or other contaminants, while smoke detectors are of course reliable only in normally clean atmospheres.

Harsh environments requiring built-in fire protection systems include certain types of machinery such as those operating in the vicinity of potentially flammable materials, such as hydraulic fluid, contained under high pressure. Afire protection system for an application of this kind must not only be hardy and free of susceptibility to false alarm, but should be capable of shutting down or otherwise modifying the machinery or associated equipment in order to at least dampen a detected fire condition.

A known fire protection system, which is disclosed in Australian patent specification 131942, employs a pneumatically operable electrical switch. The switch is triggered by a tubular detector housing decomposable gas evolving material such as a pyrotechnic fuse and itself controls electrical circuitry for operating an alarm or an automatic fire extinguisher, or for preventing overheating in mechanical or electrical equipment. It has now been appreciated that the prior system can be advantageously simplified to attain enhanced reliability of operation at reduced cost.

The invention accordingly provides a fire protection system comprising: afire extinguisher; pneumatically operable actuation means on the fire extinguisher for triggering the extinguisher by releasing extinguishant therefrom; and an elongate tube containing a temperature responsive gas-evolving substance; wherein said tube is connected to said actuation means buy a conduit for transmitting gas pressure to the actuation means; and wherein said gas-evolving substance is selected to generate, when the temperature about the tube attains a critical value within a predictable range, a quantity of gas which develops a pressure in said conduit sufficient to operate said actuation means.

Said tube may be steel, preferably copper plated and hot tinned, and may be closed at one end by a steel plug welded to the tube. Said gas evolving substance is selected with regard to the rate of response desired, and to the overall volume and pressure requirements of the system. Suitable substances include igniter fuses, a cotton wick impregnated with blackpowder, and nitrocellulose solution which has been poured into the tube and allowed to dry. For fire sensitive purposes, effective gas generation should occur when the temperature about the tube exceeds a critical temperature in the range 150"to 250"C, preferably about 200 C.

The tube may be coupled to the conduit in an arrangement which includes a frangible diaphragm for sealing offthetube. Said conduit may be branched to transmit the gas pressure to other pneumatically operable devices such as electric switches for alarms or rams disposed to modify machinery being protected, such as by closing fuel or air valves or the like.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a fire protection system in accordance with the invention; Figure 2 is an axial cross-section of the detector component of the system shown in Figure 1; Figure 3 is a side elevational view of the extinguisher component of the system shown in Figure 1; Figure 4 is an axial cross-section of the head portion of the extinguisher; and Figures 5 and 6 depict, in axial cross-sectional view two alternative constructions of the extinguisher head portion.

The basic components of the illustrated fire protection system include a fire extinguisher 8, a fire detection tube 10 containing a temperature responsive gas evolving substance 40, a pneumatically operable actuation means 18 on extinguisher 8 for triggering the extinguisher and a conduit 16 connected by a coupling 14 to detector l0fortransmit- ting gas pressure to actuation means 18. Conduit 16 may be branched as shown by broken lines to transmit the gas pressure to other pneumatically operable devices such as a pneumatic electrical switch 1 8a or a pneumatic ram 1 8c operatively associated with machinery under protection (not shown).

In a practical application, conduit system 16 and its branches may be part of a network of interconnected conduits joining one or more detectors 10 to one or more devices including at least fire extinguisher actuation means 18. Detectors 10 may be mounted at critical points about machinery such as diesel engine plant and ram 1 8c may be positioned, for example, to close fuel or air supply lines to the plant.

Detector 10 comprises a tube 12 which may be between a few centimetres and 25 metres or more in length and which may be straight (Figure 2) or bent as appropriate. It is preferably of copper plated, hot tinned steel, closed at one end by a steel plug 22 welded into the mouth of the tube. The other end of tube 12 is flared at 24 to seat between matching annular tapered surfaces 26, 28 formed on the end of an adaptor 14a and sleeve 14b which make up coupling 12. Sleeve 14b is internally lipped at one end to afford surface 28 and internally screw threaded at the other end to complement a screw threaded spigot portion 34 of adaptor 14a. Adaptor 14a includes a second spigot portion 35 which is clamped to conduit 16 by a further sleeve 14c. To seal off and protecttheinterioroftube 12, afrangible diaphragm 30 is also clamped between surfaces 26, 28.

The interior oftube 12 contains a full or partial fill 40 of a temperature responsive gas evolving substance. Suitable substances include fast or slow igni terfuses, cotton wick impregnated with blackpowder and dried nitrocellulose solution. The substance including its quantity, is selected to match a temperature range, say 1500 to 250 C, at which a response is desired, as well as the overall dimensions of the system and the number, type and distance of the actuators to be operated.When a critical temperature within the chosen range, for example about 2000C, is attained about tube 12, substance 40 reacts, typically explosively, generating gas which breaches diaphragm 30 and fills conduit 16 and its branches to develop a gas pressure sufficient to operate the associated pneumatic devices including actuating means 18, switch 18a and ram 18c.The required pressure may, for example, be in the range 150 to 3,000 P.S.I. or more.

In a modification of the illustrated arrangement, adaptor 14a may carry an electrically operable fuse mounted at the inner face of diaphragm 30 for heating fill 40 and so allowing the detector to be manually triggered.

Referring now to Figures 3 and 4, fire extinguisher 8 includes a high pressure vessel 50 for extinguishant and a head 52 atop the vessel. The head has a nipple 54 welded to vessel 50 about a port 55 in the vessel. Nipple 54 is externally screw threaded to receive an internally screw threaded socket portion 56a of an upstanding cover 56 which defines an outlet passageway 58 for extinguishant. This passageway is closed by a tubular plug member 60 which screwthreadingly engages the interior of nipple 54 at its lower, open end and is closed by a solid partition 62 at its other end. An annular lip 64 on plug member 60 engages under a corresponding shoulder 66 on cover 56.

At its upper end, plug member 60 carries an O-ring 67 for sealing its engagement with cover 56. Actuation means 18 is located just below O-ring 67, and partition 62, and comprises an annularzone 68 of plug member 60 of reduced cross-section and a surrounding matching annular cavity 70. Cavity 70 communicates via port 72 in cover 56 with a coupling assembly 74 secured to conduit 16. Assembly 74 is similar two coupling 14.

Transmittal of sufficient pressure via conduit 16 and port 72 to cavity 70 will be effective to rupture zone 68. The severed partition 62 will be forced upwardly by the pressurized extinguishant, which thus released may then pass laterally via port 76 to associated ducting (not shown).

Figures 5 and 6, in which like reference numerals indicate like parts, depict alternative extinguishers and activating means. In the Figure 5 arrangement a cover 56' is again screw-threadingly engaged, albeit internally, with a nipple 54' welded to vessel 50'. A differential piston 78 is held against an O-ring seat 80 about an extinguishant outlet passageway 58' by extinguishant back pressure leaked via a capillary 80 in the piston. Paired O-rings 82 prevent loss of back pressure extinguishant.

Piston 78 is released by opening a bleed valve 84 to leak the back pressure to atmosphere at 86. To effect this, actuating means 78' comprises a plunger 88 moveable to open the bleed valve by pneumatic pressure applied via conduit 16to a broad back face 88a ofthe plunger in a sealed cylinder 90 In the Figure 6 embodiment, an open topped cover 56" is again engaged with a nipple 54" secured by welding to vessel 50". In this case, a plunger 88" exposed at its back face 88a" to pneumatic pressure in conduit 16 acts on a latch 92 which in an overcentre latching position holds down a closure member 94 on an O-ring seat 80" in passageway 58". Closure member 94 comprises an arm 96 pivoted at 96a and suspending an annularly stepped closure plate 98 by an adjustable ball-type bearing 100.

In a further embodiment ofthe invention, not illustrated, the extinguishant outlet passageway is closed by a hollow cap of somewhat smaller diameterthan the plug member shown in Figure 4. The cap includes an annular frangible zone of reduced thickness and is arranged to be sheared off in this zone by a plunger responsive to pneumatic pressure in a detector connected conduit.

In a still further embodiment, a pneumatically responsive plunger is connected by a crank arm to a rotary valve positioned in the extinguishant outlet passageway.

Claims (11)

1. Afire protection system comprising: a fire extinguisher; pneumatically operable actuation means on the fire extinguisherfortriggering the extinguisher by releasing extinguishant therefrom; and an elongate tube containing a temperature responsive gas-evolving substance; wherein said tube is connected to said actuation means by a conduit for transmitting gas pressure to the actuation means; and wherein said gas-evolving substance is selected to generate, when the temperature about the tube attains a critical value within a predictable range, a quantity of gas which develops a pressure in said conduit sufficient to operate said actuation means.

2. Afire protection system according to claim 1 wherein said tube is coupled to said conduit in an arrangement which includes a frangible diaphragm for sealing off the tube.

3. Afire protection system according to claim 1 or 2 wherein said gas-evolving substance is selected from igniter fuses, blackpowder impregnated wicks, and nitrocellulose fill.

4. Afire protection system according to claim 1,2 or 3 wherein the critical temperature is between 150 and 250"C.

5. Afire protection system according to any preceding claim wherein said tube is a steel tube closed at one end by a steel plug welded to the tube.

6. A fire protection system according to any preceding claim wherein said conduit is branched to transmit the gas pressure to other pneumatically operable devices.

7. A fire protection system according to any preceding claim wherein said actuation means comprises a plunger moveable by pneumatic pressure to trigger the extinguisher.

8. Afire protection system according to claim 7 wherein the extinguisher includes a closure plate normally held by a latch in a position closing an outlet passageway for extinguishant and wherein said plunger is disposed to be moveable to act on the latch to release the closure plate.

9. A fire protection system according to claim 7 wherein said extinguisher includes a piston normally held by extinguishant back-pressure in a position closing an outlet passageway for extinguishant, and a bleed valve for relieving said back pressure, wherein said plunger is disposed to be moveable to open said bleed valve and so release said piston.

10. Afire protection system according to any one of claims 1 to 6 wherein the actuation means comprises a frangible zone of reduced cross-section in a tubular plug member of the extinguisher, a cavity adjacent said zone, and a port in the extinguisher for communicating pressure in said conduit to the cavity to rupture said zone.

11. A fire protection system as hereinbefore described with reference to the accompany drawings.